The present invention relates to virtual reality systems which provide simulated three dimensional images to an observer. More particularly, the present invention relates to method and apparatus for improving the appearance of the image viewed in a virtual reality system having a partially overlapped binocular display.
"Virtual reality" is a phrase that has been used to describe the experience of living or playing in a computer simulated environment which models a three dimensional ("3-D") virtual space (i.e., a virtual world). In virtual reality systems, an observer typically dons a set of goggle-mounted video screens or some other form of head mounted device ("HMD") on which the observer sees images of virtual world scenes.
In addition to military and commercial simulations, virtual reality systems have applicability in the entertainment industry and other areas as well. For, example, computer games, video arcade games and theme park attractions presenting a virtual reality experience through an HMD can provide an observer with a high level of fantasy and enjoyment. HMD's also can be used as advanced computer workstation displays and operator displays for telepresence and teleoperation of robotic devices, and in educational applications.
Several aspects of the design of an HMD may have substantial impact on its suitability for a particular application. For a theme park attraction presenting a virtual reality experience, for example, such aspects include the image quality and the angle of the field of view subtended by presented images. It is particularly desirable in theme park attractions and other entertainment applications that the HMD present images which are free of distracting cosmetic problems. In addition, a wide field of view (preferably greater than 50.degree.) is desirable because an observer's sense of immersion in a virtual world increases rapidly as more of his or her peripheral vision is stimulated.
Unfortunately, enlarging the field of view of an optical system results in increased weight and increased cost, as well as decreased eye-relief (the distance between an observer's eye and the lens system), decreased viewing volume (the region of viewing space in which the observer can see the full image) and decreased resolution.
Some HMD designs have attempted to overcome some of these drawbacks by partially overlapping the left eye and right eye fields of view, instead of providing full binocular projection. This can be accomplished by shifting the optical axis of each eyepiece towards the midline, while fixing the focal plane, or by splaying the left and right focal planes away from each other. A typical HMD with partial overlap might have two 60.degree. fields overlapped 40.degree., achieving a total perceived field of view of 80.degree. (two 20.degree. monocular fields plus the 40.degree. binocular field). Because the brain will fuse the left and right eye fields of view into a single image, this partial overlap permits an 80.degree. field to be displayed using 60.degree. optics (which are lighter and less expensive, with greater eye relief, viewing volume and resolution than corresponding 80.degree. optics).
As one might expect, the attainment of increased field of view through partial overlap is not itself without drawbacks. The principal disadvantage is a "bar" that is superimposed on the central region of the image. This bar is actually a composite virtual image of the binocular boundaries of the left and right eye images. In a typical partially overlapped binocular display, the image viewed by the observer comprises a central binocular region flanked by left and right monocular regions. The sharply focused left and right boundaries of the central binocular region may be visually distracting and objectionable to some observers. This effect may be referred to as "binocular rivalry" or "retinal rivalry". When the binocular boundaries of the left and right eye images are circular, the bar effect is known as "luning".
Some observers report that "bar" effects diminish with repeated use. However, in many applications, such as theme park entertainment, observers do not have substantial previous experience with such systems and may find the "bar" distracting or objectionable. It is thus desirable in entertainment applications to provide an image in which such effects are minimized or eliminated so an observer may readily enjoy a virtual reality experience.
In one previously known attempt to reduce binocular rivalry in partially overlapped binocular displays, a false contour line corresponding to the binocular boundaries is used to reduce the retinal rivalry of the discrepant left and right eye images. This false contour line, which may be implemented with either an electronically generated video mask, or a mechanical reticle situated in a focal plane, introduces artificial contours into the left and right images, making it appear that there is a post or other real object that is visible to both eyes.
The major drawback of this technique is that the false contours are located in the focal planes of the left and right eye images and are intentionally very conspicuous. Thus, although retinal rivalry may be reduced, observers will still perceive noticeable and distracting obstructions. For some applications, such as military aircraft displays, these obstructions might be acceptable, but for applications such as entertainment, where a sense of immersion is essential, visual obstructions are intrusive and may significantly detract from the quality of the experience.
It would therefore be desirable to greatly reduce the noticeability of the binocular boundaries of the left and right fields of view of a partially overlapped HMD.
It would also be desirable to provide an aesthetically pleasing, wide field-of-view image using medium field-of-view optics, and thereby realize the full benefits of partial overlap in an HMD.